Atomic layer etching on microdevices and nanodevices

ABSTRACT

The present invention relates to the unexpected discovery of novel methods of preparing nanodevices and/or microdevices with predetermined patterns. In one aspect, the methods of the invention allow for engineering structures and films with continuous thickness equal to or less than 50 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. § 371 national phase applicationof, and claims priority to, International Application No.PCT/US2017/034532, filed May 25, 2017, which claims priority under 35U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/341,394,filed May 25, 2016, all of which-applications are hereby incorporatedherein by reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under grant numberW911NF-14-C-0007 awarded by the U.S. Army Research Office. Thegovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

Micro-electromechanical systems (MEMS) devices comprise componentsbetween about 1-100 μm in size (i.e., 0.001-0.1 mm), and MEMS devicesgenerally range in size from 20 μm to 1.0 mm. Such devices can beprepared using modified semiconductor device fabrication technologies,which are commonly used to make electronics. Patterning of the device isusually achieved using techniques such as lithography, photolithography,etching processes (e.g., wet etching using, for example, potassiumhydroxide, tetramethylammonium hydroxide, or hydrogen fluoride; dryetching using, for example, vapor etching with xenon difluoride orhydrogen fluoride, or plasma etching), electrodischarge machining, andother technologies capable of manufacturing small devices.

Nano-electromechanical systems (NEMS) devices comprise components thathave at least one dimension less than about 1 μm in size. Many of thesedevices have been carbon based, specifically diamond, carbon nanotubesand graphene. Key problems preventing the commercial application ofnano-electromechanical devices have included low-yields, high devicequality variability and general difficulties in material compatibilitywith current nanofabrication methods.

Atomic layer deposition (ALD) uses automated cycling of component gasesto deposit solid materials conformally on solid surfaces. The growth ofindividual layers is a self-limiting reaction, resulting in lineargrowth of material, which is dependent upon the number of cycles towhich a substrate is exposed. ALD allows thickness control andconformality unmatched by any other available industrial process.Moreover, ALD processes generally employ low temperatures, with typicaldeposition temperatures below 200° C. ALD materials currently availableinclude ceramics (Al₂O₃, TaN, SiO₂, HfO₂, MgO, MnO), metals (W, Pt, Ru),semiconductors (ZnO, AlN), and various other inorganic materials. In thecase where ALD processes generate amorphous polymer structures throughsequential reactions that include organic molecules, this process iscalled molecular layer deposition (MLD), and allows controlled conformaldeposition of an additional range of materials. In many cases, ALD formssmooth, continuous films only after a number of nucleation cycles. This“nucleation period” varies from substrate to substrate, each of whichhaving a minimum thickness for the formation of a continuous film layer.In many cases, ALD forms continuous films only after tens of cycles,thus precluding engineering of conformal films thinner than a fewnanometers. For example, W ALD requires about 10 cycles of nucleation onSiO₂, but only a few cycles on Al₂O₃ to start growing. It shows lineargrowth, and should be pinhole free at about 2 nm (about 10 cycles) onAl₂O₃. On H-passivated Si, metal oxide films can take tens of cyclesbefore reaching a linear growth regime (ZrO₂: 50-60 cycles, HfO₂: 25-30cycles).

There is a need in the art for novel methods of preparing nanodevicesand/or microdevices. Such methods should allow for preparation ofdevices with specific structures and/or predetermined patterns. Thepresent invention meets this need.

BRIEF SUMMARY OF THE INVENTION

The invention provides methods of generating a microdevice or nanodevice(“micro/nanodevice”) comprising a first solid material layer. Theinvention further provides methods of smoothing surfaces on amicro/nanodevice using ALE. The invention further provides methods ofreducing a feature size of a 3D architecture on a micro/nanodevice usingALE. The invention further provides micro/nanodevices comprising anexposed solid material layer. The invention further providesmicro/nanodevices that have been smoothed using ALE. The inventionfurther provides micro/nanodevices wherein at least one feature size ofa 3D architecture thereof has been reduced using ALE.

In certain embodiments, the invention provides a microdevice ornanodevice comprising an exposed solid material layer that has anapproximately uniform thickness of ≤50 nm. In other embodiments, theinvention provides a microdevice or nanodevice comprising an exposedsolid material layer that has an approximately uniform length and/orwidth of ≥1 μm.

In certain embodiments, the microdevice or nanodevice is an absorbingmechanism for a microbolometer. In other embodiments, the microdevice ornanodevice is a bolometer, transducer, temperature sensor, heater,thermistor, microbolometer, microphone, speaker, ultrasonic transducer,resistor, inductor, spiral inductor, mechanical actuator, flagellum,flagellum motor, freestanding nanodevice, freestanding microdevice,Bragg reflector, Bragg filter, antenna, terahertz detector,electromagnetic transformer, or electrical system. In yet otherembodiments, the microdevice or nanodevice is a transistor, via,conduit, and any other electrical circuit components, Josephsonjunction, superconducting device, electrical conductor, photovoltaic,transistor, diode, waveguide, electrical transmission line, lightemitting diode, thermocouple, mirror, absorber for photons (e.g.infrared, terahertz, x-ray, gamma-ray, ultraviolet, visible light),photon emitter (e.g. infrared, terahertz, x-ray, gamma-ray, ultraviolet,visible light), radiation shield (e.g. electromagnetic or ionizing), orradiation detector (e.g. electromagnetic or ionizing). In yet otherembodiments, the microdevice or nanodevice is a nanotube, nanowire,coaxial wire, hollow tube with nanoscale diameters, periodic structure,or metamaterial.

In certain embodiments, the bolometer of the invention has low thermaltime constant, such as, in a non-limiting example, ≤10 ms. In otherembodiments, the bolometer of the invention has sheet resistance about≤150 ohm/sq. In yet other embodiments, the bolometer of the inventionhas curl about ≤250 nm.

In certain embodiments, the method comprises providing a solidsupporting material layer, wherein at least a portion of a surface ofthe solid supporting material layer is attached to a first solidmaterial layer. In other embodiments, the method comprises performingALE on at least one exposed surface of the first solid material layer.

In certain embodiments, the micro/nanodevice's first solid materiallayer has an approximately uniform thickness of ≤50 nm. In otherembodiments, the thickness is selected from the group consisting of ≤40nm, ≤30 nm, ≤20 nm, ≤10 nm, ≤8 nm, ≤6 nm, ≤4 nm, ≤2 nm, and ≤1 nm. Inyet other embodiments, the micro/nanodevice's first solid material layerhas length and/or width that is/are independently selected from thegroup consisting of ≥1 μm, ≥2 μm, ≥4 μm, ≥6 μm, ≥8 μm, ≥10 μm, ≥20 μm,≥40 μm, ≥60 μm, ≥80 μm, and ≥100 μm.

In certain embodiments, at least a portion of the first solid materiallayer is fabricated using a procedure selected from the group consistingof atomic layer deposit (ALD), micromachining, molecular layerdeposition (MLD), reactive ion beam deposition, chemical vapordeposition, sputtering, evaporation, sol-gel processing, electroplating,photopolymerization, three-dimensional (3D) printing, spin coating,spray coating, contact adhesion, casting, self-assembly, dip-coating,Langmuir-Blodgett deposition, and plasma enhanced chemical vapordeposition.

In certain embodiments, the first solid material layer comprises two ormore at least partially overlapping layers. In other embodiments, thefirst solid material layer comprises three at least partiallyoverlapping layers. In yet other embodiments, at least one of the two ormore at least partially overlapping layers is not significantly etchedby ALE.

In certain embodiments, at least a portion of the first solid materiallayer is at least partially attached to the solid supporting materiallayer through an intervening material layer. In other embodiments, atleast one selected from the group consisting of the solid supportingmaterial layer and the intervening material layer is not significantlyetched by ALE.

In certain embodiments, the first solid material layer is deposited ontothe solid supporting material layer and/or intervening material layerusing at least one method selected from the group consisting of ALD,MLD, reactive ion beam deposition, chemical vapor deposition,sputtering, evaporation, sol-gel processing, electroplating,photopolymerization, 3D printing, spin coating, spray coating, contactadhesion, casting, self-assembly, dip-coating, Langmuir-Blodgettdeposition, and plasma enhanced chemical vapor deposition.

In certain embodiments, the intervening material layer is deposited ontothe solid supporting material layer using at least one method selectedfrom the group consisting of ALD, MLD, reactive ion beam deposition,chemical vapor deposition, sputtering, evaporation, sol-gel processing,electroplating, photopolymerization, 3D printing, spin coating, spraycoating, contact adhesion, casting, self-assembly, dip-coating,Langmuir-Blodgett deposition, and plasma enhanced chemical vapordeposition.

In certain embodiments, the first solid material layer comprises atleast one material selected from the group consisting of Ag, Al, Al₂O₃,Au, Co, Cu, Fe, GaN, Ge, GeO₂, HfO₂, indium tin oxide, Ir, Mo, Ni, Pd,Pt, Rh, Ru, Ru, RuO₂, Si, SiC, SiGe, SiO₂, SnO₂, Ta, Ti, TiN, TiO₂,V₂O₅, VO_(x), W, ZnO, ZrO₂, parylene, polyimide, polymethyldisiloxane,polystyrene, polypropylene, poly(methyl methacrylate), polyethylene, anepoxy, and poly(vinyl chloride).

In certain embodiments, the nanodevice or microdevice is at leastpartially freestanding. In other embodiments, at least a portion of theintervening solid material layer is further removed. In yet otherembodiments, upon removal of at least a portion of the intervening solidmaterial layer, at least a portion of the ALE-treated first solidmaterial layer does not contact (is suspended over) the solid supportingmaterial layer.

In certain embodiments, before ALE is performed on at least one exposedsurface of the first solid material layer, the method comprises maskingat least a portion of the exposed surface of the first solid materiallayer. In other embodiments, before ALE is performed on at least oneexposed surface of the first solid material layer, the method comprisescoating the exposed surface of the first solid material layer with anALE-resistant material, and then etching the ALE-resistant material, soas to expose at least a portion of the surface of the first solidmaterial layer. In yet other embodiments, the etching is anisotropic.

In certain embodiments, the solid supporting material layer comprisesSi, SiO₂, SiGe, Pyrex, Si₃N₄, sapphire, GaAs, SiC, metal, insulator,semiconductor, or solid organic material (such as, but not limited to,polyimide). In other embodiments, the solid supporting material layer isa wafer. In yet other embodiments, the wafer comprises Si, SiO₂, SiGe,Pyrex, Si₃N₄, sapphire, GaAs, SiC, metal, insulator, semiconductor, orsolid organic material.

In certain embodiments, the masking comprises at least one selected fromthe group consisting of photolithography, electron-beam (e-beam)lithography, nanoimprint lithography, x-ray lithography, a hard maskcomprising an organic material, and a hard mask comprising an inorganicmaterial layer. In other embodiments, the masking or anisotropic etchingallows for the ALE to form a cavity within the first solid materiallayer. In yet other embodiments, the masking exposes a section of thesurface of the first solid material layer.

In certain embodiments, ALE is performed to form a cavity that islocated on the surface of the exposed first solid material layer and isapproximately hemi-spherical. In other embodiments, removal of at leasta portion of the intervening solid material layer forms a curved surfacein the nanodevice or microdevice. In yet other embodiments, theanisotropic etching creates an indentation within the first solidmaterial layer. In yet other embodiments, the surface of the indentationis further partially coated with an ALE-resistant material, such that atleast a portion of the surface of the indentation is exposed. In yetother embodiments, ALE is performed to form a cavity that is locatedwithin the first solid material layer and is approximately spherical. Inyet other embodiments, the ALE-treated first solid material layer isfurther coated. In yet other embodiments, the coating is performed usingat least one method selected from the group consisting of ALD, MLD,reactive ion beam deposition, chemical vapor deposition, sputtering,evaporation, sol-gel processing, electroplating, photopolymerization, 3Dprinting, spray coating, contact adhesion, casting, self-assembly,dip-coating, Langmuir-Blodgett deposition, and plasma enhanced vapordeposition.

In certain embodiments, the first solid material layer comprises a firstmetal-containing material. In other embodiments, the ALE comprises: (a)contacting the exposed first solid material layer with a gaseous secondmetal-containing precursor, wherein the second metal-containingprecursor comprises at least one ligand selected from the groupconsisting of a monodentate ligand, chelate and any combinationsthereof, whereby a first metal-containing precursor is formed. In yetother embodiments, the ALE comprises: (b) contacting the material formedin step (a) with a halogen-containing gas, whereby a first metal halideis formed. In yet other embodiments, the ALE comprises: (c) optionallyrepeating steps (a) and (b) one or more times. In yet other embodiments,in at least one time point selected from the group consisting of: duringstep (a), inbetween step (a) and step (b), during step (b), andinbetween step (b) and step (a) of the following iteration, the exposedfirst solid material layer is treated with an agent that promotesremoval of at least a fraction of any ligand, or any residual surfacespecies that results from a surface reaction, that is bound to and/oradsorbed onto the exposed first solid material layer.

In certain embodiments, the monodentate ligand comprises at least oneselected from the group consisting of alkyl, hydride, carbonyl, halide,alkoxide, alkylamide, silylamide and any combinations thereof. In otherembodiments, the chelate comprises at least one selected from the groupconsisting of β-diketonate, amidinate, acetamidinate, β-diketiminate,diamino alkoxide, metallocene and any combinations thereof.

In certain embodiments, step (a) and/or step (b) is/are performed at atemperature that is equal to or greater than a value ranging from about25° C. to about 450° C. In other embodiments, the gaseous compound ofthe second metal in step (a) and the halogen-containing gas in step (b)are contained in separate systems, and the nanodevice or microdevice isphysically moved from one system to the other.

In certain embodiments, the first metal-containing material comprises atleast one selected from the group consisting of metal oxide, metalnitride, metal phosphide, metal sulfide, metal arsenide, metal fluoride,metal silicide, metal boride, metal carbide, metal selenide, metaltelluride, elemental metal, metal alloy, hybrid organic-inorganicmaterial, and any combinations thereof. In other embodiments, beforestep (a) takes place, the elemental metal is converted to thecorresponding metal halide.

In certain embodiments, the exposed first solid material layer is firstsubmitted to a chemical treatment that results in the formation, on atleast a portion of the surface of the exposed first solid materiallayer, of a metal-containing material selected from the group consistingof a metal oxide, metal nitride, metal phosphide, metal sulfide, metalarsenide, metal fluoride, metal silicide, metal boride, metal carbide,metal selenide, metal telluride, elemental metal, metal alloy, hybridorganic-inorganic material, and any combinations thereof.

In certain embodiments, the first metal comprises at least one selectedfrom the group consisting of Al, Hf, Zr, Fe, Ni, Co, Mn, Mg, Rh, Ru, Cr,Si, Ti, Ga, In, Zn, Pb, Ge, Ta, Cu, W, Mo, Pt, Cd, Sn and anycombinations thereof. In other embodiments, the second metal comprisesat least one selected from the group consisting of Sn, Ge, Al, B, Ga,In, Zn, Ni, Pb, Si, S, P, Hf, Zr, Ti and any combinations thereof.

In certain embodiments, the β-diketonate comprises at least one selectedfrom the group consisting of acac (acetylacetonate), hfac(hexafluoroacetylacetonate), tfac (trifluroacetylacetonate), thd(tetramethylheptanedionate) and any combinations thereof.

In certain embodiments, the halogen-containing gas comprises a hydrogenhalide. In other embodiments, the hydrogen halide comprises HF, HCl, HBror HI.

In certain embodiments, the halogen-containing gas comprises at leastone selected from the group consisting of F₂, ClF₃, NF₃, SF₆, SF₄, XeF₂,Cl₂, Br₂, BCl₃, I₂ and any combinations thereof. In other embodiments,the halogen-containing gas comprises at least one selected from thegroup consisting of F₂, ClF₃, NF₃, SF₆, SF₄, XeF₂, Cl₂, Br₂, BCl₃, I₂,CF₄, CF₂Cl₂, CCl₄, CF₃Cl, C₂F₆, CHF₃ and any combinations thereof, andwherein the halogen-containing gas is ionized in a plasma to produce atleast one halogen radical and/or ion. In yet other embodiments, thehalogen-containing gas is ionized in a plasma to produce at least onehalogen radical and/or ion.

In certain embodiments, the exposed first solid material layer ispretreated by sequentially contacting with a gaseous secondmetal-containing precursor, and a halogen-containing gas.

BRIEF DESCRIPTION OF THE FIGURES

For the purpose of illustrating the invention, there are depicted in thedrawings certain embodiments of the invention. However, the invention isnot limited to the precise arrangements and instrumentalities of theembodiments depicted in the drawings.

FIG. 1 illustrates a general schematic of Al₂O₃ ALE surface chemistryusing Sn(acac)₂ (tin(II) acetylacetonate) and HF. (Step A) The surfaceof Al₂O₃ is converted to an AlF₃ surface layer through a fluorinationreaction. (Step B) The metal fluoride layer exchanges ligands with theSn(acac)₂ producing volatile species, which removes the AlF₃ surfacelayer.

FIGS. 2A-2B illustrate ultra-thin ALD test structures. FIG. 2A:Microbridge with Al contact pads for thermal time constant measurementspre- and post-ALE. FIG. 2B: Microbolometer-type absorption structuremade up of Al₂O₃/W/Al₂O₃ as fabricated pre-ALE.

FIGS. 3A-3B illustrate X-ray reflectivity (XRR) data for thermal ALE ofAl₂O₃ using Sn(acac)₂/HF and TMA/HF chemistries. Differences in theperiodicity for pre- and post-ALE correspond to varied X-rayinterference due to changes in the film thickness. FIG. 3A: TheSn(acac)₂/HF chemistry corresponded to about 0.022 nm/cycle etch rate.FIG. 3B: The TMA/HF chemistry at 300° C. corresponded to about 0.055nm/cycle etch rate.

FIG. 4 illustrates the finding that ALE reduces thermal time constantsof microbridges by material removal. After 140 cycles of ALE, about halfof the total Al₂O₃ thickness was removed. After 280 cycles of ALE, allof the Al₂O₃ thickness was removed leaving just Ru. Curve fitscorrespond to the extraction of thermal diffusivity (left to right:shown in black, red, and blue).

FIGS. 5A-5D illustrate thermal ALE trials on microbolometer-typeabsorption structures with Sn(acac)₂/HF chemistry (FIG. 5B) and TMA(trimethylaluminum)/HF chemistry (FIG. 5D). FIG. 2B corresponds to astructure obtained with heating and no ALE. FIG. 5A: control forSn(acac)₂/HF ALE process; no ALE with 16 hours at 200° C. FIG. 5B: 67cycles of Sn(acac)₂/HF. FIG. 5C: control for TMA/HF process; no ALE, but16 hours at 300° C. FIG. 5D: 51 cycles of TMA/HF. All structures are 16μm×16 μm and viewed at a tilt in a scanning electron microscope (SEM).

FIG. 6 illustrates ALE selectivity results for TMA/HF for Al₂O₃ and W.XRR results show that the top layer of Al₂O₃ was completely etched aftera 10% overetch and an expected layer of native WO₃ formed.

FIG. 7 illustrates an example of a lithography process using ALE tocreate Al₂O₃ nanowires (step 3) or W nanotubes with an Al₂O₃ core andshell (step 4).

FIG. 8 illustrates an example of how ALE can be used to make micro/nanobowls (step 2) or wineglass structures (step 6) out of a W ALD film.

FIG. 9 illustrates an example of how thermal ALE can be used toisotropically etch and precisely define molds for suspended tube-likestructures for waveguide applications. Current methods for thermal ALEof Al₂O₃ are selective in the presence of ALD W. The ALD waveguidematerial may include, but is not limited to, ALD W.

FIG. 10 illustrates an ultra-thin 2.5 nm Al₂O₃ suspended structureetched using TMA/HF ALE at 200° C. The beams are 4 μm (top) and 2 μm(bottom) in width with lengths from about 10-80 μm. In the bottomfigure, the red line (single line, on top) corresponds to the centerlineof a suspended beam, while the blue lines (double lines, on bottom)correspond to the edges of a suspended beam.

FIG. 11 illustrates baseline 17 μm “umbrella” (anchored) pixels.

FIG. 12 illustrates progressive removal of ALD Al₂O₃ on top/underside ofsuspended ALD Al₂O₃/W/Al₂O₃ umbrella (anchored) structure. (a) Firststep of etching resulting in negligible upwards curling. (b) Second stepof etching resulting in notable upwards curling and initiation of“potato chipping”. (c) Third step of etching resulting in full curledand “over curled” potato-chipped” structures.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the unexpected discovery of novelmethods of preparing nanodevices or microdevices with predeterminedpatterns. In one aspect, the methods of the invention allow forengineering structures and films with continuous thickness as low as 1-2Å. As demonstrated herein, atomic layer etching (ALE) was performed onsuspended nanodevices, which were fabricated using an atomic layerdeposition (ALD) on polyimide process. Two thermal ALE chemistries,including Sn(acac)₂/HF and TMA/HF, were used to remove Al₂O₃ fromsuspended microbridges and microbolometer-type absorption structures.Measurement of the thermal time constants of several microbridges afterALE was used to evaluate finite Al₂O₃ material removal. ALE can havesubstantial influence on a wide variety of microdevices. The presentdisclosure demonstrates ALE's functionality for fabrication ofultra-thin suspended structures.

The last few decades have seen immense advances in micromachiningtechnologies, and the nano/micro-electromechanical systems (N/MEMS)industry continues to push forward. As device thicknesses continue toshrink to several nanometers, precise etching processes for successfuldevice fabrication are required. Additionally, the stringent demands ofprecise tolerances for three-dimensional finFET (Fin Field EffectTransistor) devices require extremely precise, low-damage etchingprocesses. Yet many current material removal techniques, such asmilling, reactive-ion etching (RIE), and/or wet etching, are allvulnerable to manufacturing uncertainties at the nanoscale. Currentplasma processing approaches expose devices to large particle fluxescausing damage to surfaces. Etch rates of not only the desired material,but also of the underlying and masking films, must be knownOver/under-etching can lead to decreased performance or complete loss offunctionality. Techniques such as ALE, which is based on sequential,self-limiting surface reactions, allow for a more controlled etch, butthe majority of ALE processes reported use excitation methods, such asion-enhanced or energetic noble gas atom-enhanced reactions, which arenot compatible with many N/MEMS devices.

Similar to ALD, thermal ALE provides self-limiting, conformal, andatomically precise layer by layer removal of material throughthermodynamically favorable vapor phase reaction cycles. The lowertemperature requirements of thermal ALE are highly compatible withN/MEMS systems and commercial electronics manufacturing processes. ALEhas been identified as one of the leading low-damage processtechnologies for transistor development and offers unique opportunitiesfor nanodevice and microdevice fabrication. However, while in principleALE can be considered as ALD in reverse, it is not a simple reversal ofthe chemical reactions. Different precursors must be used in the removalof material. The majority of ALE to date (non-thermal ALE) has usedion-enhancement or energetic neutral atom beam enhanced surfacereactions together with halogenation of the surface to etch thematerial. These techniques can lead to anisotropic etching that may notbe desirable in some applications.

Thermal ALE can be performed based on spontaneous thermal chemistries.For example, etching of Al₂O₃ may be achieved by an initial reactantfluorinating the surface to form a metal fluoride layer. A second metalreactant can then accept fluorine from the metal fluoride and donate aligand to the metal in the metal fluoride to form volatile speciesthrough a ligand-exchange process. For example, the removal of Al₂O₃ isachieved using tin(II) acetylacetonate (Sn(acac)₂) and HF as thereactants. The overall reaction is:Al₂O₃+6HF+6Sn(acac)₂→2Al(acac)₃+6SnF(acac)+3H₂O

A schematic showing the individual Sn(acac)₂ and HF reactions is givenin FIG. 1 . The metal fluoride ligand exchange mechanism for etching canbe extended to other chemistries as well, including trimethylaluminum(TMA) and HF.

ALD allows for preparing conformal coatings for three-dimensional (3D)structures. The ability to remove material by single atomic layersconformally on 3D structures also offers extreme control in many etchingprocesses for N/MEMS. As an example, using ALE for microbolometerfabrication allows the removal of excess mass, reducing the total heatcapacity and improving sensitivity to absorbed radiation. ALD can beused to prepare a microbolometer-type absorption structure, as well asany structure where it is advantageous to remove redundant materialpost-release or from complex 3D structures.

As described herein, the present invention uses ALE in a microdevice ornanodevice fabrication process. ALE allows fine control of devicepatterning and material thicknesses, and allows access tobetter-controlled material layers than ALD during film deposition.

High Precision

N/MEMS devices often require highly uniform parts to function properly.Even small non-uniformities can result in device failure. Fabricationuncertainties in both deposition and etching can lead to difficulties inreliability and in commercialization of these devices. ALE allows foreliminating much of the uncertainty in etching. For example, ALE can beused in conjunction with ALD to create highly precise gaps less than afew nanometers in size. ALD can be used to create highly uniform andcontrollable spacing in N/MEMS devices with Ångstrom-level control. ALEcan then be used to controllably etch the ALD film, resulting in ahighly uniform gap with very low fabrication uncertainty.

Etching Freestanding Structures

Thermal ALE can be used to uniformly and controllably etch suspended,freestanding, or untethered structures (FIG. 4 ). This allows forprecise control and tunability of parameters such as size, thermal mass,curl, and stress at the end of a lithography and suspension process. Onuntethered solid structures in multiphase flow, ALE provides a precisemeans to refine or modify these structures in parallel simultaneouslyacross numerous (for example, trillions of) devices.

As demonstrated elsewhere herein, suspended fixed-fixed cantileverstructures comprising ALD Al₂O₃/Ru/Al₂O₃, as well as suspended anchoredstructures comprising ALD Al₂O₃/W/Al₂O₃, can be etched. Suspendedanchored structures can be further etched in their freestanding state.FIG. 12 demonstrates three etch steps with progressively more ALD Al₂O₃removal by thermal ALE using trimethylaluminum (TMA) and hydrogenfluoride (HF) at 300° C. Etch rates were varied due to variableprecursor pressure, resulting in more or less fluorination of the Al₂O₃surface during the fluorination and ligand exchange process used bythermal ALE of Al₂O₃. Progressively more ALD Al₂O₃ was removed from thefreestanding ALD Al₂O₃/W/Al₂O₃ anchored structure, which corresponded toincreasing upwards curl of the structure.

Qualitatively, this further confirms removal of Al₂O₃ through thermalALE from suspended ALD Al₂O₃/W/Al₂O₃, because these structures havesensitive stress gradients, to within changes on the order of singlenm's of ALD Al₂O₃. As Al₂O₃ is removed, the stress gradient becomesunbalanced resulting in upwards curl. Upon almost complete removal ofthe ALD Al₂O₃(FIG. 12 , panel c) the structures reduce to a“potato-chipped” strain relief state of curled and over −90° curledcorners.

Elimination of Over/Under-Etch

Thermal ALE has Angstrom-level control along with high uniformity andcan be used to precisely etch a material without over-etching eitherwith or without an etch stop. This provides the following benefitsversus other etch processes used in microfabrication andnanofabrication: reduce heat capacity by minimizing thickness of etchstop layers; reduce device failure due to uncontrolled or non-uniformetch processes; increase uniformity and predictability of etching;simplify production steps by eliminating or minimizing etch stop layers.

Mask Layer Undercutting and Atomic Precision Fabrication

Thermal ALE can provide an isotropic etch with Angstrom-level (atomic)precision, and is thus useful for improving the precision of isotropicetches. One example of this is in undercutting of material masked byphoto-resist (a soft mask), or another material with high etchselectivity (a hard mask). Because of the precision controlled by thenumber of ALE cycles, ALE can be used to improve the resolution offabrication using lithography.

In certain non-limiting embodiments, if lithography can be used toprovide a patterned resist, or patterned liftoff mask (metallic ornon-metallic), with features that are highly precise in position butwhose minimum feature size is 10 nm, subsequent ALE steps can be used toundercut the mask edges by a controlled number of atomic steps. Thisallows definition of features with widths on the order of Ångstroms. Inthis sense, the lithography limit is no longer the limiting factor infinal device dimensions. This method provides a parallelized fabricationprocess for generation of ≤1 nm lateral dimensions in a device. Thismethod can be used in combination with any lithographic technique,including but not limited to nanoimprint lithography, e-beamlithography, and photolithography.

Furthermore, use of ALE to enhance precision of lithographic methodsallows top-down directed, parallel fabrication at levels of precisionthat generally are not otherwise possible with any other known process.ALE-enhanced fabrication is inherently a fabrication process that treatslarge areas simultaneously. Similarly, self-assembled nanoparticles andviruses, among other structures, can form ordered arrays on a surface,and these as well can be used as masks for ALE of the underlyingsubstrate, thereby creating ordered structures in the substratedependent on the masking array.

Deposit and Etch Back

Thin films often require a period of nucleation before a smoothpinhole-free layer is formed. This is true even for ALD coatings, andcan lead to films needing to be thicker than desired in order to havethe required film properties for a micro or nano device. ALE can be usedin conjunction with a thin film deposition technique, so that films canbe grown past their nucleation regime and then etched back to a desiredthickness using ALE. This allows for a conformal film of much thinnerfinal thickness than even an ALD process can provide. It can alsoimprove properties, such as electrical conductivity and roughness, ofultra-thin films.

Deposit, Anneal, and Etch Back

Often, thin films require annealing to create a desired film morphologyor physical film property. Films ≤10 nm often agglomerate during highertemperature anneals, destroying the overall film structure. Bydepositing a thicker film (≥10 nm) with various deposition methods(including, but not limited to, chemical vapor deposition, sputtering,evaporation or plasma enhanced vapor deposition, or ALD), it is possibleto anneal the film without agglomeration. Thermal ALE can then beutilized to etch the annealed film to sub-10 nm thicknesses. This methodoffers ultra-thin films (≤10 nm) with superior physical properties thanthose obtained with a thin film deposition and anneal process.

High Aspect Ratio Etch

ALD is a self-limiting gas phase technique that shows superbconformality in high-aspect ratio structures. Similarly, thermal ALE canbe used to uniformly etch high-aspect ratio structures allowing for etchconformality at lower temperatures than currently possible. Onenon-limiting example is to etch deep vias.

Selective Etching

Since ALE consists of self-limiting surface reactions, only certainsurfaces can react in such a way that leads to etching. With the correctchoice of chemical precursors, extremely high etching selectivity ispossible (see FIGS. 5A-5B). For example, subsequent exposures of tin(II)acetylacetonate (Sn(acac)₂) and hydrogen fluoride (HF) can be used toetch Al₂O₃ films at 200° C. This same chemistry does not, however, etchan ALD W film or ALD Ru film at the same temperature, as evidenced by nomass loss during quartz crystal microbalance (QCM) experiments or metalremoval in pre- and post Al₂O₃ ALE XRR measurements. Additionally,subsequent exposures of trimethylaluminum (TMA) and HF can be used toetch Al₂O₃ films at 300° C. This same chemistry does not, however, etchan ALD W film at the same temperature, as evidenced by pre- and postAl₂O₃ ALE XRR measurements.

Definitions

As used herein, each of the following terms has the meaning associatedwith it in this section.

As used herein, unless defined otherwise, all technical and scientificterms generally have the same meaning as commonly understood by one ofordinary skill in the art to which this invention belongs. Generally,the nomenclature used herein and the laboratory procedures in surfacechemistry are those well-known and commonly employed in the art.

As used herein, the articles “a” and “an” refer to one or to more thanone (i.e. to at least one) of the grammatical object of the article. Byway of example, “an element” means one element or more than one element.

As used herein, “Å” is the abbreviation for “Ångstrom,” and 1 Å=1Ångstrom=0.1 nm=10⁻¹⁰ m=0.1 billionth of a meter.

As used herein, the term “about” will be understood by persons ofordinary skill in the art and will vary to some extent on the context inwhich it is used. As used herein, “about” when referring to a measurablevalue such as an amount, a temporal duration, and the like, is meant toencompass variations of ±20%, ±10%, ±5%, ±1%, or ±0.1% from thespecified value, as such variations are appropriate to perform thedisclosed methods.

As used herein, the term “acac” refers to acetylacetonate.

As used herein, the term “ALD” refers to atomic layer deposition, whichis a thin film deposition method. In certain embodiments, the term“thin” refers to a range of thickness from about 0.1 nm to about 300 nm.ALD uses a self-limiting reaction sequence that deposits films indiscrete steps limited by surface site chemical reactions. ALD producescontinuous films with atomically controlled thicknesses, highconformality, and typically pinhole-free and atomically smooth surfaces.These are essential properties as design constraints push devicetechnologies to ever-smaller sizes. In certain embodiments, molecularlayer deposition (MLD) is a non-limiting example of ALD. In otherembodiments, materials prepared using ALD include materials preparedusing MLD. In yet other embodiments, MLD comprises deposition of analkoxide polymer on a substrate. In yet other embodiments the MLDcomprises generation of a polymer by alternating reactions of chemicalsselected from a first and a second group; wherein the first groupincludes but is not limited to trimethylaluminum, titaniumtetrachloride, and diethyl zinc; and wherein the second group includesbut is not limited to ethylene glycol, propylene glycol, glycerol,hydroquinone, 1,2-ethanedithiol, and 1,3-propanedithiol.

As used herein, the term “ALE” refers to atomic layer etching. The terms“ALE” and “Atomic Layer Etching” as used herein refer to any etchingprocess based on cyclic etching of a substrate by two or more chemicalreagents, thereby removing a controlled thickness of the exposedsubstrate with each cycle of etching. Such processing can thus beaccomplished in liquid phase environments, gas environments, or plasmaenvironments, and can apply both to etching of inorganic compounds andto removal of monomers of a polymer or other organic materials.

As used herein, the term “exposed” as applied to a surface refers to thefact that the surface can be contacted with a fluid, such as a gasand/or a liquid.

As used herein, the term “finFET” refers to Fin Field Effect Transistor.

As used herein, the term “instructional material” includes apublication, a recording, a diagram, or any other medium of expressionthat may be used to communicate the usefulness of the compositionsand/or methods of the invention. In certain embodiments, theinstructional material may be part of a kit useful for generating acomposition and/or performing the method of the invention. Theinstructional material of the kit may, for example, be affixed to acontainer that contains the compositions of the invention or be shippedtogether with a container that contains the compositions. Alternatively,the instructional material may be shipped separately from the containerwith the intention that the recipient uses the instructional materialand the compositions cooperatively. For example, the instructionalmaterial is for use of a kit; instructions for use of the compositions;or instructions for use of the compositions.

As used herein, the term “MEMS” refers to a micro-electromechanicalsystem.

As used herein, the term “metal chelate” refers to a compound formedbetween a metal and at least one chelating (or polydentate) ligand. Incertain embodiments, the chelating ligand is at least one selected fromthe group consisting of β-diketonate, thio-β-diketonate, amidinate,acetamidinate, β-diketiminate and (substituted or non-substituted)cyclopentadienyl. In other embodiments, all the chelating ligands in themetal chelate complex are identical (e.g., all groups areβ-diketonates). In other embodiments, at least two distinct chelatingligands are present in the chelate.

As used herein, the term “metal precursor” refers to a metal chelate, ametal monodentate complex and any combinations thereof.

As used herein, the term “metal monodentate complex” refers to acompound formed between a metal and at least one monodentate ligand. Incertain embodiments, the monodentate ligand is at least one selectedfrom the group consisting of alkyl, hydride, carbonyl (carbon monoxide),halide, alkoxide, alkylamide and silylamide. In other embodiments, allthe monodentate ligands in the metal monodentate complex are identical(e.g., all alkyl groups are methyl). In other embodiments, at least twodistinct monodentate ligands are present in the monodentate complex(e.g., the alkyl groups comprise methyl and ethyl).

As used herein, “μm” is the abbreviation for “micron” or “micrometer”,and 1 μm=0.001 mm=10⁻⁶ m=1 millionth of a meter.

As used herein, a “nanodevice” refers to a device that has at least onecomponent with at least one spatial dimension less than 1 micron.

As used herein, the term “NEMS” refers to a nano-electromechanicalsystem.

As used herein, “nm” is the abbreviation for “nanometer” and 1 nm=1nanometer=10⁻⁹ m=1 billionth of a meter.

As used herein, the term “QCM” refers to quartz crystal microbalance.

As used herein, the term “RIE” refers to reactive-ion etching.

As used herein, the term “TMA” refers to trimethylaluminum.

As used herein, the term “ultra-thin” as applied to a layer refers to alayer that has thickness equal to or less than ≤100 nm, such as forexample ≤50 nm.

As used herein, the term “XRR” refers to X-ray reflectivity.

Throughout this disclosure, various aspects of the invention may bepresented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible sub-ranges as well asindividual numerical values within that range and, when appropriate,partial integers of the numerical values within ranges. For example,description of a range such as from 1 to 6 should be considered to havespecifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, and so on, as well asindividual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5,5.3, and 6. This applies regardless of the breadth of the range.

Compositions

The invention provides a microdevice or nanodevice obtained according tothe methods of the invention. In certain embodiments, the microdevice ornanodevice comprises at least one ultra-thin layer.

The microdevice or nanodevice of the invention can be prepared accordingto any of the methods of the invention. Each and every embodimentdescribed as relating to a method of the invention is equally envisionedfor a microdevice or nanodevice of the invention. Each and everyembodiment described as relating to a microdevice or nanodevice of theinvention is equally envisioned for a method of the invention.

In certain embodiments, the invention provides a microdevice ornanodevice comprising an exposed solid material layer that has anapproximately uniform thickness of ≤50 nm. In other embodiments, theinvention provides a microdevice or nanodevice comprising an exposedsolid material layer that has an approximately uniform length or widthof ≥1 m.

In certain embodiments, the microdevice or nanodevice is an absorbingmechanism for a microbolometer. In other embodiments, the microdevice ornanodevice is a bolometer, transducer, temperature sensor, heater,thermistor, microbolometer, microphone, speaker, ultrasonic transducer,resistor, inductor, spiral inductor, mechanical actuator, flagellum,flagellum motor, freestanding nanodevice, freestanding microdevice,Bragg reflector, Bragg filter, antenna, terahertz detector,electromagnetic transformer, or electrical system. In yet otherembodiments, the microdevice or nanodevice is a transistor, via,conduit, and any other electrical circuit components, Josephsonjunction, superconducting device, electrical conductor, photovoltaic,transistor, diode, waveguide, electrical transmission line, lightemitting diode, thermocouple, mirror, absorber for photons (infrared,terahertz, x-ray, gamma-ray, ultraviolet, visible light), photon emitter(infrared, terahertz, x-ray, gamma-ray, ultraviolet, visible light),radiation shield (electromagnetic or ionizing), or radiation detector(electromagnetic or ionizing). In yet other embodiments, the microdeviceor nanodevice is a nanotube, nanowire, coaxial wire, hollow tube withnanoscale diameters, periodic structure, or metamaterial.

In certain embodiments, the bolometer of the invention has low thermaltime constant, such as, in a non-limiting example, ≤10 ms. In otherembodiments, the bolometer of the invention has sheet resistance about≤150 ohm/sq. In yet other embodiments, the bolometer of the inventionhas curl about ≤250 nm.

In certain embodiments, the bolometer of the invention comprises ananchored structure comprising a laminate structure, which comprises abottom dielectric layer, a middle conductor layer, and a top dielectriclayer. In other embodiments, the bottom dielectric layer has a thicknessof ≤50 or ≤30 or ≤10 Ångstroms. In yet other embodiments, the bottomdielectric layer comprises Al₂O₃. In yet other embodiments, the middleconductor layer has a thickness of ≤250 Ångstroms. In yet otherembodiments, the middle conductor layer comprises W and/or Ru and/orgraphene. In yet other embodiments, the top dielectric layer has athickness of ≤50 or ≤30 or ≤10 Ångstroms. In yet other embodiments, thetop dielectric layer comprises Al₂O₃.

In certain embodiments, the bolometer of the invention comprises a legstructure comprising a laminate structure, which comprises a bottomdielectric layer, a middle conductor layer, and a top dielectric layer.In other embodiments, the bottom dielectric layer has a thickness of ≤50or ≤30 or ≤10 Ångstroms. In yet other embodiments, the bottom dielectriclayer comprises Al₂O₃. In yet other embodiments, the middle conductorlayer has a thickness of ≤50 or ≤30 or ≤10 Ångstroms. In yet otherembodiments, the middle conductor layer has a thickness of ≤250Ångstroms. In yet other embodiments, the middle conductor layercomprises Ti and/or Ru. In yet other embodiments, the top dielectriclayer has a thickness of ≤50 or ≤30 or ≤10 Ångstroms. In yet otherembodiments, the top dielectric layer comprises Al₂O₃.

In certain embodiments, the bolometer of the invention comprises atransducing element structure comprising a laminate structure, whichcomprises a bottom dielectric layer, a middle transducer layer, and atop dielectric layer. In other embodiments, the bottom dielectric layerhas a thickness of ≤50 or ≤30 or ≤10 Ångstroms. In yet otherembodiments, the bottom dielectric layer comprises Al₂O₃. In yet otherembodiments, the middle transducer layer has a thickness of ≤1500 or≤750 or ≤350 Ångstroms. In yet other embodiments, the middle transducerlayer has a thickness of ≤2,500 Ångstroms. In yet other embodiments, themiddle transducer layer comprises VO_(x). In yet other embodiments, thetop dielectric layer has a thickness of ≤50 or ≤30 or ≤10 Ångstroms. Inyet other embodiments, the top dielectric layer comprises Al₂O₃.

Methods

The invention provides a method of generating a microdevice ornanodevice (micro/nanodevice) comprising a first solid material layer.In certain embodiments, the method comprises providing a solidsupporting material layer, wherein at least a portion of a surface ofthe solid supporting material layer is attached to a first solidmaterial layer. In other embodiments, the method comprises performingALE on at least one exposed surface of the first solid material layer.

In certain embodiments, the micro/nanodevice's first solid materiallayer has an approximately uniform thickness of ≤50 nm. In otherembodiments, the thickness is selected from the group consisting of ≤40nm, ≤30 nm, ≤20 nm, ≤10 nm, ≤8 nm, ≤6 nm, ≤4 nm, ≤2 nm, and ≤1 nm. Inyet other embodiments, the micro/nanodevice's first solid material layerhas length and width that are independently selected from the groupconsisting of ≥1 μm, ≥2 μm, ≥4 μm, ≥6 μm, ≥8 μm, ≥10 μm, ≥20 μm, ≥40 μm,≥60 μm, ≥80 μm, and ≥100 μm.

In certain embodiments, at least a portion of the first solid materiallayer is fabricated using a procedure selected from the group consistingof ALD, micromachining, MLD, reactive ion beam deposition, chemicalvapor deposition, sputtering, evaporation, sol-gel processing,electroplating, photopolymerization, 3D printing, spin coating, spraycoating, contact adhesion, casting, self-assembly, dip-coating,Langmuir-Blodgett deposition, and plasma enhanced chemical vapordeposition.

In certain embodiments, the first solid material layer comprises two ormore at least partially overlapping layers. In other embodiments, thefirst solid material layer comprises three at least partiallyoverlapping layers. In yet other embodiments, at least one of the two ormore at least partially overlapping layers is not significantly etchedby ALE.

In certain embodiments, at least a portion of the first solid materiallayer is at least partially attached to the solid supporting materiallayer through an intervening material layer. In other embodiments, atleast one selected from the group consisting of the solid supportingmaterial layer and the intervening material layer is not significantlyetched by ALE.

In certain embodiments, the first solid material layer is deposited ontothe solid supporting material layer and/or intervening material layerusing at least one method selected from the group consisting of ALD,MLD, reactive ion beam deposition, chemical vapor deposition,sputtering, evaporation, sol-gel processing, electroplating,photopolymerization, 3D printing, spin coating, spray coating, contactadhesion, casting, self-assembly, dip-coating, Langmuir-Blodgettdeposition, and plasma enhanced chemical vapor deposition.

In certain embodiments, the intervening material layer is deposited ontothe solid supporting material layer using at least one method selectedfrom the group consisting of ALD, MLD, reactive ion beam deposition,chemical vapor deposition, sputtering, evaporation, sol-gel processing,electroplating, photopolymerization, 3D printing, spin coating, spraycoating, contact adhesion, casting, self-assembly, dip-coating,Langmuir-Blodgett deposition, and plasma enhanced chemical vapordeposition.

In certain embodiments, the first solid material layer comprises atleast one material selected from the group consisting of Ag, Al, Al₂O₃,Au, Co, Cu, Fe, GaN, Ge, GeO₂, HfO₂, indium tin oxide, Ir, Mo, Ni, Pd,Pt, Rh, Ru, Ru, RuO₂, Si, SiC, SiGe, SiO₂, SnO₂, Ta, Ti, TiN, TiO₂,V₂O₅, VO_(x), W, ZnO, ZrO₂, parylene, polyimide, polymethyldisiloxane,polystyrene, polypropylene, poly(methyl methacrylate), polyethylene, anepoxy, and poly(vinyl chloride).

In certain embodiments, the nanodevice or microdevice is at leastpartially freestanding. In other embodiments, at least a portion of theintervening solid material layer is further removed. In yet otherembodiments, upon removal of at least a portion of the intervening solidmaterial layer, at least a portion of the ALE-treated first solidmaterial layer does not contact (is suspended over) the solid supportingmaterial layer.

In certain embodiments, before ALE is performed on at least one exposedsurface of the first solid material layer, the method comprises (a)masking at least a portion of the exposed surface of the first solidmaterial layer. In other embodiments, before ALE is performed on atleast one exposed surface of the first solid material layer, the methodcomprises coating the exposed surface of the first solid material layerwith an atomic layer etching (ALE)-resistant material, and then etchingthe ALE-resistant material, so as to expose at least a portion of thesurface of the first solid material layer. In yet other embodiments, theetching is anisotropic.

In certain embodiments, the solid supporting material layer comprisesSi, SiO₂, SiGe, Pyrex, Si₃N₄, sapphire, GaAs, SiC, a metal, aninsulator, a semiconductor, or a solid organic material (e.g.polyimide). In other embodiments, the solid supporting material layer isa wafer. In yet other embodiments, the wafer comprises Si, SiO₂, SiGe,Pyrex, Si₃N₄, sapphire, GaAs, SiC, a metal, an insulator, asemiconductor, or a solid organic material.

In certain embodiments, the masking comprises at least one selected fromthe group consisting of photolithography, e-beam lithography,nanoimprint lithography, x-ray lithography, a hard mask comprising anorganic material, and a hard mask comprising an inorganic materiallayer. In other embodiments, the masking or anisotropic etching allowsfor the ALE to form a cavity within the first solid material layer. Inyet other embodiments, the masking exposes a section of the surface ofthe first solid material layer.

In certain embodiments, ALE is performed to form a cavity that islocated on the surface of the exposed first solid material layer and isapproximately hemi-spherical. In other embodiments, removal of at leasta portion of the intervening solid material layer forms a curved surfacein the nanodevice or microdevice. In yet other embodiments, theanisotropic etching creates an indentation within the first solidmaterial layer. In yet other embodiments, the surface of the indentationis further partially coated with an ALE-resistant material, such that atleast a portion of the surface of the indentation is exposed. In yetother embodiments, ALE is performed to form a cavity that is locatedwithin the first solid material layer and is approximately spherical. Inyet other embodiments, the ALE-treated first solid material layer isfurther coated. In yet other embodiments, the coating is performed usingat least one method selected from the group consisting of ALD, MLD,reactive ion beam deposition, chemical vapor deposition, sputtering,evaporation, sol-gel processing, electroplating, photopolymerization, 3Dprinting, spray coating, contact adhesion, casting, self-assembly,dip-coating, Langmuir-Blodgett deposition, and plasma enhanced vapordeposition.

In certain embodiments, the first solid material layer comprises a firstmetal-containing material. In other embodiments, the ALE comprises (a)contacting the exposed first solid material layer with a gaseous secondmetal-containing precursor, wherein the second metal-containingprecursor comprises at least one ligand selected from the groupconsisting of a monodentate ligand, chelate and any combinationsthereof, whereby a first metal-containing precursor is formed. In yetother embodiments, the ALE comprises (b) contacting the material formedin step (a) with a halogen-containing gas, whereby a first metal halideis formed. In yet other embodiments, the ALE comprises (c) optionallyrepeating steps (a) and (b) one or more times. In yet other embodiments,in at least one time point selected from the group consisting of: duringstep (a), inbetween step (a) and step (b), during step (b), andinbetween step (b) and step (a) of the following iteration, the exposedfirst solid material layer is treated with an agent that promotesremoval of at least a fraction of any ligand, or any residual surfacespecies that results from a surface reaction, that is bound to and/oradsorbed onto the exposed first solid material layer.

In certain embodiments, the monodentate ligand comprises at least oneselected from the group consisting of alkyl, hydride, carbonyl, halide,alkoxide, alkylamide, silylamide and any combinations thereof. In otherembodiments, the chelate comprises at least one selected from the groupconsisting of β-diketonate, amidinate, acetamidinate, β-diketiminate,diamino alkoxide, metallocene and any combinations thereof.

In certain embodiments, step (a) and/or step (b) is/are performed at atemperature that is equal to or greater than a value ranging from about25° C. to about 450° C. In other embodiments, the gaseous compound ofthe second metal in step (a) and the halogen-containing gas in step (b)are contained in separate systems, and the nanodevice or microdevice isphysically moved from one system to the other.

In certain embodiments, the first metal-containing material comprises atleast one selected from the group consisting of metal oxide, metalnitride, metal phosphide, metal sulfide, metal arsenide, metal fluoride,metal silicide, metal boride, metal carbide, metal selenide, metaltelluride, elemental metal, metal alloy, hybrid organic-inorganicmaterial, and any combinations thereof. In other embodiments, beforestep (a) takes place, the elemental metal is converted to thecorresponding metal halide.

In certain embodiments, the exposed first solid material layer is firstsubmitted to a chemical treatment that results in the formation, on atleast a portion of the surface of the exposed first solid materiallayer, of a metal-containing material selected from the group consistingof a metal oxide, metal nitride, metal phosphide, metal sulfide, metalarsenide, metal fluoride, metal silicide, metal boride, metal carbide,metal selenide, metal telluride, elemental metal, metal alloy, hybridorganic-inorganic material, and any combinations thereof.

In certain embodiments, the first metal comprises at least one selectedfrom the group consisting of Al, Hf, Zr, Fe, Ni, Co, Mn, Mg, Rh, Ru, Cr,Si, Ti, Ga, In, Zn, Pb, Ge, Ta, Cu, W, Mo, Pt, Cd, Sn and anycombinations thereof. In other embodiments, the second metal comprisesat least one selected from the group consisting of Sn, Ge, Al, B, Ga,In, Zn, Ni, Pb, Si, S, P, Hf, Zr, Ti and any combinations thereof.

In certain embodiments, the β-diketonate comprises at least one selectedfrom the group consisting of acac (acetylacetonate), hfac(hexafluoroacetylacetonate), tfac (trifluroacetylacetonate), thd(tetramethylheptanedionate) and any combinations thereof.

In certain embodiments, the halogen-containing gas comprises a hydrogenhalide. In other embodiments, the hydrogen halide comprises HF, HCl, HBror HI.

In certain embodiments, the halogen-containing gas comprises at leastone selected from the group consisting of F₂, ClF₃, NF₃, SF₆, SF₄, XeF₂,Cl₂, Br₂, BCl₃, I₂ and any combinations thereof. In other embodiments,the halogen-containing gas comprises at least one selected from thegroup consisting of F₂, ClF₃, NF₃, SF₆, SF₄, XeF₂, Cl₂, Br₂, BCl₃, I₂,CF₄, CF₂Cl₂, CCl₄, CF₃Cl, C₂F₆, CHF₃ and any combinations thereof, andwherein the halogen-containing gas is ionized in a plasma to produce atleast one halogen radical and/or ion. In yet other embodiments, thehalogen-containing gas is ionized in a plasma to produce at least onehalogen radical and/or ion.

In certain embodiments, the exposed first solid material layer ispretreated by sequentially contacting with a gaseous secondmetal-containing precursor, and a halogen-containing gas.

In certain embodiments, the invention provides methods of smoothingsurfaces using ALE, as well as provides surfaces that are smooth byvirtue of the use of ALE. Smoothing of surfaces is of interest in thesemiconductor industry. Smoothing may be used to obtain damage-freelayers. Sputtering can be used to remove some materials, but can leave arough, damaged surface. ALE can be used to remove the damaged layer andsmooth the surface to produce a “damage-free surface.”

Surface smoothing can also be used to obtain very high quality ultrathinfilms. For example, high quality ultrathin films can be produced by a“deposit/etch back” strategy by depositing a thicker film and thenetching back to a thinner film. In a non-limiting embodiment, nucleationeffects can lead to roughness in the ultrathin deposited film; once acontinuous and pinhole-free thicker film is formed, ALE can etch thisfilm back and obtain a smoother surface than would have been produced bygrowing to this ultrathin thickness.

In certain embodiments, ALE can be used to reduce the feature size of 3Darchitectures. The gas phase, isotropic and/or anisotropic etchingobtained using thermal ALE or enhanced thermal ALE can reduce featuresizes and mass conformally with atomic level precision versus the numberof ALE reaction cycles. Applications include reducing the width ofFinFET channels in MOSFET structures and reducing the diameter and massof nanowires and quantum dots.

Every formulation or combination of components described or exemplifiedcan be used to practice the invention, unless otherwise stated. Specificnames of compounds are intended to be exemplary, as it is known that oneof ordinary skill in the art can name the same compounds differently.When a compound is described herein such that a particular isomer orenantiomer of the compound is not specified, for example, in a formulaor in a chemical name, that description is intended to include eachisomer and/or enantiomer of the compound described individual or in anycombination. Although the description herein contains many embodiments,these should not be construed as limiting the scope of the invention butas merely providing illustrations of some of the presently preferredembodiments of the invention.

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, numerous equivalents to thespecific procedures, embodiments, claims, and examples described herein.Such equivalents are considered to be within the scope of this inventionand covered by the claims appended hereto. For example, it should beunderstood, that modifications in reaction conditions, including but notlimited to reaction times, reaction temperature and pressure, reactionsize/volume, and experimental reagents with art-recognized alternativesand using no more than routine experimentation, are within the scope ofthe present application. In general the terms and phrases used hereinhave their art-recognized meaning, which can be found by reference tostandard texts, journal references and contexts known to those skilledin the art. Any preceding definitions are provided to clarify theirspecific use in the context of the invention.

The following examples further illustrate aspects of the presentinvention. However, they are in no way a limitation of the teachings ordisclosure of the present invention as set forth herein.

EXAMPLES

The invention is now described with reference to the following Examples.These Examples are provided for the purpose of illustration only, andthe invention is not limited to these Examples, but rather encompassesall variations that are evident as a result of the teachings providedherein.

Example 1: Suspended MicroBridge Structures

Suspended microbridge test structures were fabricated using thermal ALE(FIG. 2A). A sacrificial polyimide layer was spun onto a bare siliconwafer to a thickness of about 3 μm and cured. Next, ALD layers weredeposited using a Beneq TFS 200 ALD reactor. The layers were depositedat 300° C. in a trilayer configuration consisting of 6.15 nm Al₂O₃/3.7nm Ru/6.15 nm Al₂O₃. The Al₂O₃ was deposited using TMA and H₂Oprecursors for growth at about 0.13 nm/cycle. The Ru was deposited usingthermally activated Ru(EtCp)₂ (bis(ethylcyclopentyldienyl)ruthenium(II))at 110° C. and O₂ for growth at about 0.04 nm/cycle. The ALD layers werethen patterned using a positive photoresist mask and a CF₄/O₂ reactiveion etch chemistry. Next, using a negative photoresist lift off process,Al was evaporated to form contact pads at the anchors of themicrobridges. Finally, an O₂ plasma ashing process was used to removethe sacrificial polyimide layer and release the microbridges. Themicrobridges are on the order of 20-120 μm in length and 2-4 μm inwidth.

Microbolometer-type absorption structures (FIG. 2B) were fabricated in asimilar process as described above with the absence of Al contact pads.The layers were produced in a custom ALD W reactor and consisted of anominal Al₂O₃/W/Al₂O₃ trilayer, which produces flat suspended absorptionstructures. The Al₂O₃ deposition was performed at 130° C. for growth atabout 0.13 nm/cycle. The W deposition was performed at 130° C. forgrowth at about 0.38 nm/cycle.

Methods

Two thermal ALE chemistries etch Al₂O₃ using a fluorination and ligandexchange mechanism. Sn(acac)₂/HF and TMA/HF etch Al₂O₃ in aself-limiting process. FIGS. 3A-3B demonstrate X-ray reflectivity datafrom Al₂O₃ coated Si test wafers, providing etch rates. Etching usingSn(acac)₂/HF was performed at 200° C. with an etch rate of about 0.022nm/cycle. Etching using TMA/HF was performed at 300° C. with an etchrate of about 0.055 nm/cycle. Special attention was paid to precursordose pressure and purge times to ensure surface saturation andself-limited behavior. Etch rates are subject to change with variedreactor parameters. For example, the Sn(acac)₂/HF etch rate wasincreased to about 0.046 nm/cycle by varying dose pressures.

Micropulse calorimetry was used to measure material removal on suspendedmicrobridge test structures. This method was previously used to measurethe specific heat capacity of ALD W (Eigenfeld, et al., 2015,Transducers 2015, IEEE, Anchorage, Ak., pp. 1385-1388). The thermal timeconstants, τ's, of the microbridge test structures are measured beforeand after ALE sessions. A pulsed step voltage is applied across thebridge (with a rise time <1 μs) and a transient current response ismonitored, which is several orders of magnitude slower than the voltagerise. This effect is a result of the temperature sensitive resistanceresponding to Joule heating of the Ru and surrounding Al₂O₃ layers. Anexponential decay function can be fit to the measured current responseto extract τ for a given microbridge length. The experimental τ data canthen be fit to extract the thermal diffusivity, α, where τ is given as:τ=α·l ²/π²where l is the microbridge length and α is given as,α=κ/ρ·c _(p)where κ is the thermal conductivity, ρ is the density and c_(p) is thespecific heat capacity of the microbridge. To compare the measured timeconstant data to calculations using the expected thickness removalduring ALE processing, κ and ρ of the microbridges pre- and post-ALEwere measured following the methods outlined by Eigenfeld, et al., 2015,Nanoscale 7(42): 17923-17928. The microbridges were Joule-heated using asteady-state biasing technique and κ extracted using a temperaturedependent resistance Joule heating model. The thicknesses and densitiesof the pre-ALE ALD films were also measured using X-ray reflectometry(XRR) on a Bede D1 X-ray diffractometer. The X-ray wavelength formeasurements was 1.54 Å, corresponding to the Ka transition in the CuX-ray tube. The Bede REFS software was used to fit the XRR data andextract the thickness and densities of the ALD Al₂O₃ and Ru films. Usingthe measured κ and ρ and bulk c_(p) values, the measured thermaldiffusivity, α_(exp), may be compared with the calculated thermaldiffusivity, α_(calc), based on a relative thicknesses of Ru and Al₂O₃contributions given as,α_(calc)=(α_(Ru)·τ_(Ru)+α_(Al2O3)·τ_(Al2O3))/(τ_(Ru)+τ_(Al2O3))where t is the thickness of the Ru or Al₂O₃ layers.

Results

The τ's of several lengths of the Al₂O₃/Ru/Al₂O₃ test structures weremeasured pre-ALE and then etched using the Sn(acac)₂/HF chemistry. FIG.4 demonstrates pre and post ALE etching with Sn(acac)₂/HF. After eachALE session, the thermal time constants of the microbridges are reducedas Al₂O₃ is removed in increments of 140 and 280 Sn(acac)₂/HF cycles(FIG. 4 ). Using equation 1, α was extracted (FIG. 4 fit lines) for pre-and post-ALE sessions. Using measured κ, ρ, and bulk specific heatcapacity, α_(calc) for the first 140 ALE cycles (middle curve, FIG. 4 )using an expected 3.1 nm top and bottom Al₂O₃ etch falls within 13% ofα_(exp). For 280 ALE cycles, α_(calc) does not agree well with α_(exp),likely due to complete removal of the Al₂O₃ and oxidation of the bare Rustructure upon transfer from the ALE vacuum system to the electricalprobing vacuum system. Sources of error include slight variations inetch rates between the top and underside Al₂O₃ surfaces or the globaletch rate due to reactor parameters. It is possible longer precursorexposure would reduce such error to ensure complete underside surfacesaturation for each ALE cycle. A notable increase in resistance of theRu microbridges was observed after being exposed to atmosphere forseveral days.

The microbolometer-type absorption structures were subject to both etchchemistries to remove about 3.1 nm of Al₂O₃ on top and bottom of thestructure. The Sn(acac)₂/HF chemistry was repeated for 67 cycles at theelevated etch rate of 0.046 nm/cycle, and the TMA/HF chemistry repeatedfor 51 cycles at the typical etch rate. Additionally, the suspendedstructures were subjected to the etch duration and the given etchtemperature with no ALE processing to determine if they would survive atelevated temperature for the etch duration and remain flat (FIGS.5A-5D). The structures remained flat after being subject to both 200° C.and 300° C. for 16 hours with no ALE processing. After 67 cycles of ALEprocessing with Sn(acac)₂/HF, the structure yielded negligible curling.After 51 cycles of ALE with TMA/HF, processing also yielded negligiblecurling.

To confirm the exposed metal sidewalls of the microbridge teststructures and microbolometer-type suspended structures were not etchedduring the above experiments, each etching chemistry was tested forselectivity to Al₂O₃ in the presence of Ru and W. The top Al₂O₃ layer ina trilayer of ALD Al₂O₃/Ru/Al₂O₃ on Si was etched using Sn(acac)₂/HF at200° C., and the top Al₂O₃ layer in a trilayer of ALD Al₂O₃/W/Al₂O₃ onSi was etched using Sn(acac)₂/HF at 200° C. and TMA/HF at 300° C. Foreach etch, Al₂O₃ was removed completely, with a 10% overetch based onits thickness and ALE etch rate. The trilayer thicknesses and densitieswere measured using XRR pre- and post-ALE to determine if the Ru and Wfilms were affected by the ALE chemistries during etch exposure. FIG. 6demonstrates the results of the selectivity etch experiment forAl₂O₃/W/Al₂O₃ using TMA/HF. After etching the top Al₂O₃ layer, a thinnative metal oxide layer in the form of WO₃ or RuO₂ was formed afterexposure to atmosphere during XRR on the order of a few nanometers.Using thickness and density calculations for oxide growth, the measuredmetal oxide thicknesses via XRR correspond to the expected oxide growthfor an un-etched metal film. FIG. 6 demonstrates this result for TMA/HFat 300° C. in the presence of Al₂O₃ and W. Similar results were achievedfor Sn(acac)₂/HF at 200° C. in the presence of Al₂O₃/W and Al₂O₃/Ru.

As described herein, the first ever demonstration of thermal ALE onsuspended NEMS structures was demonstrated using Sn(acac)₂/HF and TMA/HFchemistries. Etching Al₂O₃ conformally on the top and underside ofmicrobridge test structures was confirmed using micropulse calorimetry.Etching of microbolometer-type absorption structures to reduce thermalmass and maintain a flat suspended structure was achieved using TMA/HF.The Sn(acac)₂/HF and TMA/HF chemistries were selective to Al₂O₃ in thepresence of ALD W and ALD Ru. The concept of conformal isotropic etchingof suspended NEMS structure can be applied to a variety of nichefabrication processes for future devices. ALE of a diverse subset ofmaterials opens unique avenues for microdevice and nanodevicefabrication.

Example 2: Nanotubes/Nanowires/Coaxial Wires

One application of ALE for N/MEMS is the fabrication of nanotubes ornanowires (FIG. 7 ). For example, a patterned alumina (Al₂O₃) layer ontop of polyimide can be further thinned under photoresist allowing forAngstrom-controlled etching of structures less than tens of nanometers.After release of the structure, a suspended Al₂O₃ nanowire can becreated. Further film deposition, including, but not limited to, atomiclayer deposition (ALD) of tungsten (W) on this suspended nanowire cancreate W nanotubes with an Al₂O₃ core. Capping the W layer with Al₂O₃ALD is a non-limiting effective method of preventing W oxidation.

Example 3: Micro/Nano Bowls or Wine Glass Structures

Another application for ALE on N/MEMS is the fabrication of micro/nanobowls (FIG. 8 ). One method of creating these structures is by startingwith a patterned pinhole on top of a material to be etched by thermalALE. Since thermal ALE is an isotropic etch process, etching through thepinhole creates a uniform semi-sphere in the etched material. Removal ofthe photoresist then leaves a bowl structure behind. The dimensions ofthese bowls can be easily tuned with Angstrom level control. After thebowl is completed, another film can be deposited into the bowl, such asone using an ALD process. Using a patterned photoresist to protect onlythe film inside the bowl, the film outside the bowl can be etched away.Another etch process can then remove the underlying bowl material,leaving only a suspended bowl film of thickness determined by the bowlALD layer.

Example 4: Acoustic or Optical Waveguides-Suspended Tube Structures

One application of ALE is in the fabrication of suspended tube-likestructures for waveguide applications. Suspended waveguides result inlower losses to the substrate. By using ALD Al₂O₃ or another materialwhich can be etched using thermal ALE, as a sacrificial etch layer,thermal ALE can be used to precisely define a cylindrical cavity due toits conformal and isotropic properties (FIG. 9 , step 5). A desired ALDwaveguide material can then be deposited conformally to coat theprecisely defined cavity. Another ALE etch can be used to preciselyremove the material in the stem of the cylindrical cavity (FIG. 9 , step8). These structures can be anchored or tethered to the underlyingsubstrate and complex networks formed for potential photonic or acousticwaveguide applications.

Example 5: Precise Etching of Ultra-Thin Layers

As described elsewhere herein, a precise etch of ultra-thin layers canbe achieved with no need for significant over-etching. Over-etching cancause damage to underlying layers, which can be crucial for final deviceperformance. In this example, 2.5 nm of Al₂O₃ is etched into cantileverpatterns on polyimide and the polyimide removed in an O₂ ashing processto suspend ultrathin Al₂O₃ structures.

Example 6: Microbolometer

The present invention can be applied to a microbolometer device, whichis a nano-electromechanical system. The generalizations provided hereincan be easily be extended to a broad range of N/MEMS devices.

Microbolometer Umbrella (Anchored) Structure, Support Leg Structure andTransducing Structure:

The creation of highly sensitive infrared (IR) detectors allows for ahost of imaging applications in industrial, military, and commercialapplications, including, but not limited to: monitoring of facilitiesand machinery; aerial surveillance; night vision; automotive collisionavoidance; weapon detection; non-invasive medical imaging; waterresource management; energy audits, petroleum and chemical safetymonitoring.

At present, IR imagers encompass two categories of operation,photoconductive and thermal. Photoconductive detectors, such as QuantumWell Infrared Photodetectors or photodiode devices, are consideredsingle stage transducers. They operate on the immediate electricaldetection of individual photon interactions with a material lattice.These devices require sufficient cooling for operation, making thembulky and cost ineffective. Uncooled thermal detectors, or two stagetransducers, have emerged as the dominant technology for marketable IRimaging, operating on the conversion of IR radiation to detectable heat.These devices include microbolometers, pyroelectrics, thermopiles andGolay cells. The microbolometer device emerged as the market leader forits ease of fabrication, large format compatibility and extremesensitivity with the help of modern CMOS circuitry.

A micro-bolometer pixel structure comprises three components: anabsorbing element, thermally isolating supporting element, andtransducing element. The transducing element is a resistive structurefor which minute changes in temperature, caused by thermal energytransfer from absorbed radiation by the absorber, result in minutechanges of the transducer's resistance. In order to maximize thiseffect, the absorber should be designed to absorb as much incidentinfrared radiation as possible. This is achieved by material choice, aswell as mechanical design of the pixel. A reflective layer is oftendeposited at the substrate level to enable a normally deconstructiveoptical absorbance cavity to maximize IR absorption in the absorber. Thesupporting element comprises an electro-thermal pathway to theunderlying substrate. In certain embodiments, it is designed to reducethermal loss, while also allowing a low electrical resistance connectionto the transducing element.

Conventional bolometer absorber structures comprise layers that supportand protect a resistive thin metal at ≥50 Ångstrom-thick optimized toabsorb almost all incident radiation. The combination of materials inthe laminate structure makes up a thermal mass, which experiences atemperature rise relative to the percentage of absorbed radiationconverted to thermal energy. Often, the supporting and protective layersfor the metal absorber are many orders of magnitude thicker than themetal, resulting in a very large thermal mass. This constrictstransducer's speed of response to absorbed radiation resulting inperformance loss for the pixel. One solution to reducing the absorber'sthermal mass is to introduce channels or insets that reduce the overallamount of material in the absorber.

Additionally, these thick support and protection layers in the absorberare often made of SiO₂, a material with unwanted infrared reflective andabsorption properties. This effect is magnified by the thickness of thelayer and ultimately interferes with the optical cavity formed by theabsorber and reflector layer to maximize absorption. This can result ina loss of absorbed IR power and limit the device's sensitivity.Therefore, there is a need for thinner supporting and protective layersin the absorption structure that allow for a substantial increase in thepixel's speed of response to incident radiation. Additionally, theselayers should have minimal IR optical interference to enhance thepixel's total IR absorption and therefore sensitivity.

Conventional bolometer support leg structures comprises layers thatsupport and protect a conductive metal at ≥50 Ångstrom thickness. Thepurpose of the metal layer is to electrically connect an underlyingread-out integrated circuit (ROIC) to the transducing element in thesuspended bolometer. Often, the supporting and protective layers for theconductive metal are several orders of magnitude thicker than the metalresulting in a large thermal mass. This constrains the bolometer's speedof response to absorbed radiation resulting in a performance loss of thepixel.

These thick support and protection layers in the support leg are alsooften made of SiO₂, a material with unwanted IR reflective andabsorption properties. Again, this effect is magnified by the thicknessof the layer and ultimately interferes with the optical cavity formed bythe absorber and reflector layer to maximize absorption. This can resultin a loss of absorbed IR power and limit the device's sensitivity.Therefore, there is a need for thinner supporting and protective layersin the support leg structure that will allow for a substantial increasein the bolometer's speed of response to incident radiation.Additionally, these layers should have minimal IR optical interferenceto enhance the pixel's total IR absorption and therefore sensitivity.

Conventional bolometer transducing elements consist of materials with ahigh temperature coefficient of resistance (TCR), usually in the 2-3%/Krange. Often VO_(x) or α-Si are used as transducing materials. However,during the fabrication process of the bolometer unit, a thick dielectricetch stop layer is often utilized during the transducing materialpatterning and etch step. Again, this additional material is extrathermal mass and does not serve an active bolometer material. Therefore,there is a need for a thinner etch stop/protective bottom layer for thetransducing element of the bolometer unit to further improve bolometerperformance.

Micro-Bolometer Freestanding Absorber Structure:

The present invention allows for the preparation of a bolometer devicewith an absorption structure comprising ≤30 or ≤10 Angstrom-thicksupporting and protection layers aims to reduce the device's totalthermal mass.

A non-limiting example of an absorbing structure for a microbolometercomprises an umbrella-like structure made up of atomic layer depositedmaterials. This freestanding absorber structure is spaced apart, butanchored to an underlying transducer, which is spaced apart, butanchored to the underlying ROIC (FIG. 11 ). The freestanding absorbercan be fabricated by use of an ALD on polyimide method (see U.S. PatentApplication Publication No. US20150212276, which is incorporated hereinin its entirety by reference). Specifically, the freestanding absorbercontains support and protection layers, which are thinner than theresistive metal absorber to reduce the overall thermal mass resulting ina faster speed of response for the bolometer.

The present invention enables further performance enhancement inmicrobolometers. The fabricated device can be further improved by usingthermal ALE on the freestanding absorber structure to thin thedielectric layers to ≤30 or ≤10 Ångstrom thicknesses (FIG. 5 ). Suchthicknesses are difficult or impossible to achieve directly by ALDduring the standard fabrication process or by other conventionaldeposition or etching processes. At ≤30 or ≤10 Ångstrom thicknesses, thecontribution of the dielectric layers to the overall heat capacity isvery small or almost negligible, yet the active metal absorber layerremains protected from oxidization.

In accordance with the previously described methods of bolometerperformance improvement, a bolometer with an absorption structureconsisting of ≤30 Ångstrom or ≤10 Ångstrom thick metal absorption layerhas a reduced total thermal mass as compared to the bolometers of theprior art.

In certain embodiments, the invention enables a higher performancemicrobolometer by utilizing a “deposit and etch back” technique on theactive metal absorber. Because films grown to ultra-thin (≤50 nm)thicknesses often have a large portion of their resistance attributed toelectron scattering at grain boundaries and film surfaces, theresistivity is often much higher than the bulk value. By using metal ALEit is possible to “deposit and etch back” a film to ultra-thin thicknesswhile smoothing the film roughness. The thicker film formed duringdeposition has larger grain structures that reduce grain boundaryscattering. When ALE is performed, the film is naturally smoothed,because the isotropic and self-limiting etch removes surface topographyfeatures equally from all angles. The final film has minimal grainboundary and film surface scattering. Thus, an optimal electrical sheetresistance for LWIR absorption can be achieved at thinner thicknesses,further improving the performance of the overall bolometer unit.

Micro-Bolometer Support Leg Structure:

The present invention allows for preparation of a bolometer with asupport leg structure comprising ≤10 Angstrom thick supporting andprotection layers for the metal conductor, which reduces the bolometer'stotal thermal mass.

A non-limiting example of a support leg structure for a micro-bolometercomprises serpentine-like arm comprising atomic layer depositedmaterials. FIG. 11 illustrates a complete “umbrella” type pixel whereinthe support leg structures are fabricated using non-ALD thin filmdeposition methods. This structure is spaced apart, but anchored to anunderlying ROIC and supports the transducing and absorbing elements ofthe pixel structure. In this non-limiting example, the support leg isfabricated using an ALD on polyimide method (see U.S. Patent ApplicationPublication No. US20150212276, which is incorporated herein in itsentirety by reference) to incorporate ultra-thin support and protectionlayers as well as a conductive metal for electrical connection fromunderlying circuitry of the ROIC to the pixel transducer. The supportand protection layers are thinner than the conductive metal absorber toreduce the overall thermal mass, resulting in a faster speed of responsefor the bolometer.

The present invention further provides a high-performancemicrobolometer, wherein thermal ALE is used on the suspended support legstructure to thin the dielectric layers to ≤30 or ≤10 Ångstromthicknesses. Such thicknesses are difficult or impossible to achievedirectly by ALD during the standard fabrication process or by otherconventional deposition or etching processes. At ≤30 or ≤10 Ångstromthicknesses, the contribution of the dielectric layers to the overallheat capacity is very small or almost negligible, yet the active metalleg conduction layer remains protected from oxidization. Following thepreviously discussed methods of bolometer performance improvement, abolometer with a support leg structure comprising ≤30 or ≤10 Ångstromthick metal conduction layer has a reduced total thermal mass ascompared to the bolometers of the prior art.

The present invention further provides a high-performancemicrobolometer, which is prepared using a “deposit and etch back”technique on the active metal support leg conductor. Since films grownto ultra-thin thicknesses often have a large portion of their resistanceattributed to electron scattering at grain boundaries and film surfaces,the resistivity is often much higher than the bulk value. By using metalALE it is possible to “deposit and etch back” a film to ultra-thinthickness, while also being ultra-smooth. The thicker film formed duringdeposition has larger grain structures, which reduce grain boundaryscattering. When ALE is performed, the film is naturally smoothed,because the isotropic and self-limiting etch removes surface topographyfeatures equally from all angles. In certain embodiments, the final filmhas minimal grain boundary and film surface scattering. Thus, an optimalelectrical sheet resistance for providing electrical contact to thetransducing element can be achieved at thinner thickness, furtherimproving the performance of the overall bolometer unit.

Micro-Bolometer Transducing Element:

The present invention allows for the preparation of a bolometer with atransducing element consisting of ≤30 or ≤10 Ångstrom thick supportinglayer for the transducing element, which reduces the bolometer's totalthermal mass.

Currently a thick supporting layer is required to provide enoughmaterial to safely protect the underlying materials during thetransducing element patterning and etch step. To reduce this layerthickness, the transducing material etch should be as precise aspossible. Current etching technologies lack atomic precision and thusthick etch stop layers are required during fabrication.

The present invention provides a high-performance microbolometer,wherein selective ALE process for etching the transducing material isused. By using selective ALE to etch the transducing material, there isno requirement for a thick underlying etch stop. This allows the overallthermal mass of the bolometer unit to be reduced and its performance tobe enhanced.

In accordance with the previously described methods of bolometerperformance improvement, a bolometer with a transducing elementcomprising ≤100 or ≤300 or ≤500 Ångstrom thick transducing material hasa reduced total thermal mass as compared to bolometers of the prior art.

The present invention provides a high-performance microbolometer, whichis prepared using a “deposit, anneal and etch back” technique on theactive transducing material. Since films grown to ultra-thin thicknessesoften are amorphous or have a large portion of their electricalresistance attributed to electron scattering at grain boundaries andfilm surfaces, the resistivity is often much higher than the bulk value.In certain embodiments, a post-deposition annealing step is utilized topromote crystallization or grain growth in the thin film to providepreferred electrical properties. In the case of the bolometertransducing element, properties such as high TCR, low resistivity andlow 1/f noise are desirable. However, for ultra-thin films, thispost-deposition annealing step is often damaging to the film whereinagglomeration or pin-hole formation ensues. By using selective ALE forthe transducing material, it is possible to “deposit, anneal and etchback” a film to ultra-thin thickness while also being ultra-smoothduring and after the isotropic ALE step. The annealed thick film formedhas an improved crystalline and grain structure, promoting the desiredphysical properties of high TCR, low resistivity and low 1/f noise.Producing an ultra-thin transducing material with similar performance tothe thicker version of the material offers further performanceenhancement of the bolometer unit by a continued reduction in thermalmass.

Micro-Bolometer Thin Etch Stop Layers:

In accordance with the previously described methods of using ALE to makethin etch stop layers, the application to microbolometers isspecifically stated. For any and all microbolometer layers requiring anetch, the underlying layer can be made thin if the ALE is selective tothe underlying layer and not the remaining layers. The underlyingprotective layer of the transducing element can be made thin ifselective ALE is applied to the transducing element layer, whichselectively etches the transducing element layer but does not etch theunderlying protective layer. The transducing layer's top protectivelayer can be made thin if it is etched with ALE selective to that topprotective layer and does not etch the transducer layer. The legconductive layer can be etched with selective ALE while its underlyinglayer is not etched with selective ALE.

The disclosures of each and every patent, patent application, andpublication cited herein are hereby incorporated herein by reference intheir entirety.

While the invention has been disclosed with reference to specificembodiments, it is apparent that other embodiments and variations ofthis invention may be devised by others skilled in the art withoutdeparting from the true spirit and scope of the invention. The appendedclaims are intended to be construed to include all such embodiments andequivalent variations.

What is claimed is:
 1. A method of generating a microdevice ornanodevice (micro/nanodevice), the method comprising: providing asacrificial layer and a device layer, wherein a first portion of thedevice layer is not in contact with the sacrificial layer and a secondportion of the device layer is in contact with the sacrificial layer;wherein the first portion of the device layer comprises at least a topand an underside; and performing: i) thermal atomic layer etching (ALE)on the at least top and underside of the first portion of the devicelayer; or ii) thermal ALE on the sacrificial layer; wherein, before ALEis performed on at least one exposed surface of the device layer, atleast one of the following is performed: (a) masking at least a portionof the exposed surface of the device layer; (b) coating the exposedsurface of the device layer with an atomic layer etching (ALE)-resistantmaterial, and then etching the ALE-resistant material, so as to exposeat least a portion of the surface of the device layer, wherein theetching is optionally anisotropic; and generating the micro/nanodevicecomprising the device layer.
 2. The method of claim 1, wherein at leastone applies: (a) the micro/nanodevice's device layer has a thickness of≤50 nm; (b) wherein the micro/nanodevice's device layer has length andwidth that are independently selected from the group consisting of ≥1μm, ≥2 μm, ≥4 μm, ≥6 μm, ≥8 μm, ≥10 μm, ≥20 μm, ≥40 μm, ≥60 μm, ≥80 μm,and ≥100 μm.
 3. The method of claim 1, wherein at least a portion of thedevice layer is fabricated using a procedure selected from the groupconsisting of atomic layer deposit (ALD), micromachining, molecularlayer deposition (MLD), reactive ion beam deposition, chemical vapordeposition, sputtering, evaporation, sol-gel processing, electroplating,photopolymerization, three-dimensional (3D) printing, spin coating,spray coating, contact adhesion, casting, self-assembly, dip-coating,Langmuir-Blodgett deposition, and plasma enhanced chemical vapordeposition.
 4. The method of claim 1, wherein the device layer comprisestwo or more at least partially overlapping layers, optionally wherein atleast one of the two or more at least partially overlapping layers isnot significantly etched by ALE.
 5. The method of claim 1, wherein atleast one applies: (a) the microdevice or nanodevice is an absorbingmechanism for a microbolometer; (b) the nanodevice or microdevice is atleast partially freestanding.
 6. The method of claim 1, wherein at leasta portion of the device layer is at least partially attached to thesacrificial layer through an intervening material layer, optionallywherein at least one selected from the group consisting of thesacrificial layer and the intervening material layer is notsignificantly etched by ALE, wherein at least one selected from thegroup consisting of the device layer and the intervening material isdeposited onto the sacrificial layer or intervening material layer usingat least one method selected from the group consisting of ALD, MLD,reactive ion beam deposition, chemical vapor deposition, sputtering,evaporation, sol-gel processing, electroplating, photopolymerization, 3Dprinting, spin coating, spray coating, contact adhesion, casting,self-assembly, dip-coating, Langmuir-Blodgett deposition, and plasmaenhanced chemical vapor deposition.
 7. The method of claim 1, whereinthe device layer comprises at least one material selected from the groupconsisting of Ag, Al, Al₂O₃, Au, Co, Cu, Fe, GaN, Ge, GeO₂, HfO₂, indiumtin oxide, Ir, Mo, Ni, Pd, Pt, Rh, Ru, Ru, RuO₂, Si, SiC, SiGe, SiO₂,SnO₂, Ta, Ti, TiN, TiO₂, V₂O₅, VO_(x), W, ZnO, ZrO₂, parylene,polyimide, polymethyldisiloxane, polystyrene, polypropylene, poly(methylmethacrylate), polyethylene, an epoxy, and poly(vinyl chloride).
 8. Themethod of claim 1, wherein the sacrificial layer comprises Si, SiO₂,SiGe, Pyrex, Si₃N₄, sapphire, GaAs, SiC, a metal, an insulator, asemiconductor, or a solid organic material, and optionally wherein thesacrificial layer is a wafer.
 9. The method of claim 1, wherein themasking comprises at least one selected from the group consisting ofphotolithography, electron-beam (e-beam) lithography, nanoimprintlithography, x-ray lithography, a hard mask comprising an organicmaterial, and a hard mask comprising an inorganic material layer. 10.The method of claim 1, wherein the ALE-treated device layer is furthercoated.
 11. The method of claim 1, wherein the device layer comprises afirst metal-containing material and wherein the ALE comprises: (a)contacting the exposed device layer with a gaseous secondmetal-containing precursor, wherein the second metal-containingprecursor comprises at least one ligand selected from the groupconsisting of a monodentate ligand, chelate and combinations thereof,whereby a first metal-containing precursor is formed; (b) contacting thematerial formed in step (a) with a halogen-containing gas, whereby afirst metal halide is formed; and (c) optionally repeating steps (a) and(b) one or more times; wherein, in at least one time point selected fromthe group consisting of: during step (a), in between step (a) and step(b), during step (b), and in between step (b) and step (a) of thefollowing iteration, the exposed device layer is treated with an agentthat promotes removal of at least a fraction of any ligand, or anyresidual surface species that results from a surface reaction, that isbound to or adsorbed onto the exposed device layer; wherein themonodentate ligand comprises at least one selected from the groupconsisting of alkyl, hydride, carbonyl, halide, alkoxide, alkylamide,silylamide and combinations thereof; and, wherein the chelate comprisesat least one selected from the group consisting of β-diketonate,amidinate, acetamidinate, β-diketiminate, diamino alkoxide, metalloceneand combinations thereof.
 12. The method of claim 11, wherein at leastone selected from the group consisting of step (a) and step (b) isperformed at a temperature that is equal to or greater than a valueranging from about 25° C. to about 450° C.
 13. The method of claim 11,wherein the first metal-containing material comprises at least oneselected from the group consisting of metal oxide, metal nitride, metalphosphide, metal sulfide, metal arsenide, metal fluoride, metalsilicide, metal boride, metal carbide, metal selenide, metal telluride,elemental metal, metal alloy, hybrid organic-inorganic material, andcombinations thereof; optionally wherein, before step (a) takes place,the elemental metal is converted to the corresponding metal halide. 14.The method of claim 11, wherein the exposed device layer is firstsubmitted to a chemical treatment that results in the formation, on atleast a portion of the surface of the exposed device layer, of ametal-containing material selected from the group consisting of a metaloxide, metal nitride, metal phosphide, metal sulfide, metal arsenide,metal fluoride, metal silicide, metal boride, metal carbide, metalselenide, metal telluride, elemental metal, metal alloy, hybridorganic-inorganic material, and combinations thereof.
 15. The method ofclaim 11, wherein at least one applies: the first metal comprises atleast one selected from the group consisting of Al, Hf, Zr, Fe, Ni, Co,Mn, Mg, Rh, Ru, Cr, Si, Ti, Ga, In, Zn, Pb, Ge, Ta, Cu, W, Mo, Pt, Cd,Sn, and combinations thereof; the second metal comprises at least oneselected from the group consisting of Sn, Ge, Al, B, Ga, In, Zn, Ni, Pb,Si, S, P, Hf, Zr, Ti and combinations thereof.
 16. The method of claim11, wherein at least one applies: (a) the β-diketonate comprises atleast one selected from the group consisting of acac (acetylacetonate),hfac (hexafluoroacetylacetonate), tfac (trifluroacetylacetonate), thd(tetramethylheptanedionate) and combinations thereof; (b) thehalogen-containing gas comprises a hydrogen halide; (c) thehalogen-containing gas comprises at least one selected from the groupconsisting of F₂, ClF₃, NF₃, SF₆, SF₄, XeF₂, Cl₂, Br₂, BCl₃, I₂ andcombinations thereof; (d) the halogen-containing gas comprises at leastone selected from the group consisting of F₂, ClF₃, NF₃, SF₆, SF₄, XeF₂,Cl₂, Br₂, BCl₃, I₂, CF₄, CF₂Cl₂, CCl₄, CF₃Cl, C₂F₆, CHF₃ andcombinations thereof, and wherein the halogen-containing gas is ionizedin a plasma to produce at least one halogen radical or ion.
 17. Themethod of claim 11, wherein the exposed device layer is pretreated bysequentially contacting with a gaseous second metal-containingprecursor, and a halogen-containing gas.